Thru repeated tries to 3 box this fight, I found out that if you have your healers at the max range they will not be affect by his knock back.
Find the spot where your healer can still cast on you and every time he knock you back, just run back to that spot and start healing.
I 3 boxed it with a 87th lvl Sk, Clr, and Shm, only with some tier 3 items. My Sk only has about 6k ac and 52k hp